During the production of fibers for papermaking, wood or other fiber source material is ground and/or mechanically treated such that the material may be broken down further and refined into individual fibers.
High consistency disk refiners are used with stock containing eighteen to sixty percent fiber by weight. High consistency refiners are used to produce mechanical and semichemical pulp or furnish from undigested wood chips and semidigested wood chips. The refiner breaks down wood chips and clumps of wood fibers into individual fibers from which paper may be formed. After processing in a high consistency refiner, the fibers may be further processed in, for example, a low consistency refiner to improve their freeness or bonding capability.
A refiner disk consists of a disk-shaped steel or steel-alloy casting which has a multiplicity of generally radially extending bars integrally cast with and as a part of the surface of the disk. A first refiner disk is mounted on a rotor for rotation and another disk is held opposed to the first refiner disk, either by rigid mounting or by mounting on an opposite rotating rotor. The refiner disks, as they move past each other, separate and refine the wood pulp as it passes between the opposed disks.
When dealing with high consistency pulp and wood chips, the edges of the refiner bar act as cutting edges for separating fibers from wood chips or clumps of fibers and for splitting open individual fibers.
Disk refiners are used in the paper manufacturing industry to prepare the cellulose fibers of a paper pulp into a desired condition prior to delivering the pulp to the papermaking machine.
It is the purpose of a stock refiner to modify the fibers without significantly reducing the length or individual strength of these fibers. U.S. Pat. No. 3,880,368 to Matthew discloses the benefit of repeatedly and gently refining the pulp to ensure that fibers are not extensively damaged. Matthew points out the impracticability of avoiding all fiber damage, and suggests that gentle refining can be accomplished by the use of many blades per plate and operating at relatively high speeds. However, the use of many blades or bars on the plates reduces the flow area available for both fiber and the steam generated in high consistency refining. This can reduce the through-put, decreasing the efficiency and increasing the costs of the refining process.
Lower intensity refining has been obtained by increasing the number of refiner bars within a given disk area. However, the width of individual bars cannot be proportionately reduced, as inadequate bar strength may result. Bars which are too narrow for a given height will tend to crack or otherwise deviate from specified performance. Thus increasing the numbers of bars has come at the expense of the groove width and depth between neighboring bars. This reduced groove size mandates a reduced outer diameter open area, which causes high steam pressure and reduced loadability because of excessive back-flowing steam.
Refiner disks have been fabricated with steam exhaust channels which extend radially outwardly and cut across refining grooves between bars. These large-width channels provide not only a low-resistance path for the escape of steam generated in the refining process, but also a channel for unrefined fiber to exit the refining zone without being refined. The steam exhaust channels sacrifice a significant portion of refiner bar length, and hence result in a reduction from the optimum potential refining intensity.
What is needed is a refiner disk which provides improved steam flow while maintaining a refining action that is less damaging to individual paper fibers and provides optimum refining intensity.